Backing a sail is turning it so that the wind hits the front face; the effect is to slow a ship or boat. A sail which is being backed is said to be ‘aback.’ A sailing ship which accidentally goes aback when tacking loses its momentum and is said to be ‘in irons.’ A person is said to be ‘all aback’ when he is confused or surprised.

Abaft

Aft of a given point on a ship; e.g. the bridge is abaft the bow.

Acockbill

Out of alignment or awry. In original usage, if a sailing ship’s yards were not all aligned, she was said to be "all acockbill." See also SQUARED AWAY.

Active Homing

A homing (guidance) method where the missile provides its own signal (typically either radar or sonar) transmissions and homes in on the energy reflected off the target.

Adrift

(1) Not secured; scattered about; not properly stowed, or out of place. (2) (RCN) Missing in action. "Oh no, I'm adrift for the meeting and the Bossman'll be there!"

Advance and Transfer

Two separate terms involving a ship’s turn. Advance is the forward progress made between the time that the rudder is put over and the time the ship is steady on her new course. Transfer is the horizontal displacement of the ship during the same period of time. Advance is maximized in a turn of 90 degrees or more; transfer is maximized in a turn of 180 degrees or more.

Air Wing

The officers and men assigned to the aircraft aboard a ship, whether a carrier (usually referred to as a "carrier airwing") or a smaller vessel (generally referred to as an "air det" (detachment)); the airwing has a separate administrative and operational chain of command.

The betting pool on the hour and minute the ship will drop anchor or tie up.

Anchor’s at short stay

The ship has been pulled up to the anchor, but the anchor is still lying on the bottom, undisturbed.

Anchor’s aweigh

The anchor has left the bottom. Legally, at this point the ship is under way, whether or not it is "making way" (moving through the water under its own power).

Anchor’s up and down

The anchor’s flukes have broken free of the bottom, and the shank is more or less vertical. The crown of the anchor is still resting on the bottom.

ARAB

(UK) Arrogant Regular Army Bastard.

ASAP

As Soon As Possible. Usually spoken as a word, "A

Avast

A command which means, basically, "Stop what you’re doing." This term appears to be from the French "Haud Vast," literally "hold fast."

Aweigh

(sometimes seen (improperly) as "away") When a ship raises (weighs) anchor, the anchor is said to be aweigh as soon as it is no longer in contact with the sea bottom. From the process of weighing anchor; the sequence of reports is usually as follows:

AWOL Bag

A small canvas or vinyl bag used to carry clothing or personal items while on weekend liberty.